Hemodialysis urea rebound and membrane biocompatibility: accuracy of Kt/V estimations

To date, the magnitude, causes, and factors that govern urea rebound are not clearly defined. This study was undertaken to determine the possible influence of the biocompatibility of dialyzer membrane on urea rebound and to assess the participation of rebound in the calculation of Kt/V-urea by different methods. Blood urea samples were obtained before, and at 2, 30, and 60 min posthemodialysis in 8 patients undergoing dialysis with 2 different membranes, Cuprophan and polyacrylonitrile (24 sessions with each membrane). Urea rebound was documented in all patients. The degree of rebound was large, 20%, and it was achieved within 30 min after the end of dialysis. Urea rebound was observed with both Cuprophan and polyacrylonitrile membranes, without significant differences. Kt/V-urea significantly decreased (p < 0.001) by all methods when urea rebound was incorporated. We conclude that urea rebound is clinically very important and is not influenced by the biocompatibility of the dialyzer membrane. This phenomenon must be taken into account in the calculation of Kt/V; otherwise, it might be overestimated.